Magnetic properties of dense ferrofluids: an influence of interparticle correlations.

A statistical model has been developed describing the magnetostatic properties of dense ferrocolloids and the dielectric properties of polar fluids. The model is based on the relation between the magnetization and the pair correlation function of a spatially homogeneous system of dipole particles. This approach allows us to calculate the ferrofluid magnetization (polarization density of polar fluid) in a form of expansion over both the particle concentration and the potential of the interparticle dipole-dipole interaction U(d). The obtained expressions for the ferrocolloid initial magnetic susceptibility, the dielectric constant of polar fluid and the ferrofluid magnetization with the accuracy approximately U(2)(d) describe well the experimental data and the results of computer modeling. The model justifies the validity of the "modified mean-field approach," and the effective field is calculated as a function of the Langevin magnetization.